This time she did respond and the pair began sending each other more than 200 messages a day.

Judge Sweeney said an imam at a NSW mosque twice refused the man's requests to marry the pair, telling him, "this is not allowed. This is illegal".

The man then sought out another religious leader and in January 2014, arranged for a "marriage ceremony".

After the ceremony, fruit, chocolates, water and soft drink were brought out for everyone to enjoy and the man gave the girl $500 as a wedding gift.

For more than a month after the ceremony the pair had sex several times a day across various locations in NSW, often on mattresses on the floor.

In sentencing him in Sydney's District Court on Friday, Judge Sweeney rejected the man's claims that he didn't know what he was doing was illegal and said neither his cultural or religious beliefs excused his actions.

She also dismissed the argument the girl had "consented".

"She may be intelligent or articulate for a 12 or 13-year-old girl but she is still a 12-year-old girl," she said.

The man's "deliberate and determined pursuit of the girl" made it a serious offence, she said.

The court previously heard that after his arrest in February last year, the girl was taken to hospital suffering a sharp abdominal pain.

It was discovered she was having an ectopic pregnancy and miscarried.

The man, who is from Lebanon, has been in Villawood Detention centre since his arrest.

Judge Sweeney sentenced him to at least seven and a half years and a maximum of 10 for one count of the persistent sexual abuse of a child.

The man will appeal what he considers a "harsh" sentence, his barrister Alex Radojev said outside court.